1. Field of the Invention
The invention relates to powdered lacquers based on a mixture of epoxide compounds and salts of inorganic acids and optionally polyesters with primary diamines as hardeners.
2. Discussion of the Background
There is great need in industry for powdered lacquers of all kinds. This is primarily due to the fact that solvents can be avoided in the application of powdered lacquers, and only small losses occur in use. Powdered lacquers are economical and not environmentally damaging.
Most known lacquers yield glossy finishes. Recently, however, there has been greater interest in flat finishes because they require significantly less cleaning than glossy finishes. In addition, it is often more advantageous to produce flat finishes for safety reasons.
The simplest method of obtaining a flat finish is to admix smaller or larger quantities of fillers, depending on the degree of flat effect desired, such as chalk, finely ground silicon dioxide, barium sulfate, or incompatible additives such as wax, or cellulose derivatives. However, these additives result in lacquer films with poor technical characteristics.
DE-PS No. 23 24 696 discloses a method for the manufacture of coverings with a flat finish in which a special hardener--the salt of cyclic amidines with certain polycarboxylic acids--is used. In fact, due to its exceptional technical characteristics only this method has been able to succeed in the marketplace. The method has since been improved several times (see DE-OS No. 30 26 455, OS No. 30 26 456 and German Patent Application No. P 35 11 998.5 of Apr. 2, 1985 "Hardeners for Powdered Covering Agents Based on Epoxy Resins").
Nevertheless, this method has some basic disadvantages. The required amidines are expensive and not always available in the necessary quantities. It would be desirable if more readily available basic compounds, like straight liquid diamines, could be used in a suitable form as hardeners for epoxide resins. The salts of these amines with the usual acids, however, in contrast to the amidine salts, are so stable that under the baking conditions common in the powdered lacquer industry, no adequate hardening of the epoxide resins takes place.
An aqueous coating system obtained through a reaction of a polyol-polyether epoxide with phosphoric acid anhydride is described in EP-PS No. 0 082 196. An aqueous system of this type does not suggest powdered lacquers and would not help in the search for lacquer systems which produce a flat effect.